Allow uppercase variant of package root also

Both the straight-forward mod-ule_ROOT variable and the more idiomatic
MOD_ULE_ROOT variant are allowed when specifying where to look for a
package.
Allow common _ROOT suffix in addition to original _PREFIX
Consolidate package location variables

Always use the same form of package location variable, to maintain
consistency.
Use uppercase for the shared-object variable as well
Handle quoted assignment arguments with whitespace

If we are going to set e.g. CXXFLAGS to more than one value, the
quotes must be preserved at the same time as the list is laundered
(for autotools-variables)
Also clean the temporary config-var file
Reuse the uppercase variant across the entire function
Check that test prog. compiled before declared found

The previous version did the test and setting of the config variable
right, but reported that the module was found only if the files were
located, independently of the result of the compile.
Merge pull request #167 from rolk/167_quoted

Handle quoted assignment arguments with whitespace
Merge pull request #168 from rolk/168_distclean

Also clean the temporary config-var file
Merge pull request #169 from rolk/169_havetest

Check that test prog. compiled before declared found
Merge pull request #166 from rolk/166_upcase

Use uppercase consistently in configuration variable names